The production of continuous glass fibers by mechanically drawing molten streams of glass from orifices in the bottom wall of a feeder or bushing is well known. It is also known to make hollow glass fibers using this process. For example, U.S. Pat. No. 4,846,864 to Huey discloses a tip assembly for use in a bushing for the production of hollow glass fibers by a continuous process. The hollow glass fibers have more surface area for the same amount of glass, and as a result they can be more effective in thermal and acoustical insulation products.
Glass fibers are also used as reinforcements in composite materials. When a fiber reinforced composite material is subjected to stress, some of the stress is transferred from the matrix of the composite material to the stronger fibers. As a result, the composite material has greater strength than an unreinforced matrix. To effectively transfer the stress, there must be a strong bond between the fibers and the matrix. Fibers which are perfectly shaped and have a smooth surface depend on the interaction between the surface and the matrix for this bonding. Such fibers when untreated usually lack a sufficient surface interaction to form a strong bond with a matrix. Consequently, the surface of the fibers is coated with a size composition containing a coupling agent to produce a better bond between the fibers and matrix. This sizing treatment increases the cost and complexity of the manufacturing process. Also, it is difficult to coat the fibers uniformly with the size composition. When the coating is not uniform, the bond between the fibers and the matrix is weaker. Therefore, it would be desirable to provide a method for making fibers which does not depend on the coupling agent of a sizing treatment to provide a strong bond with the matrix of a composite material. The method must be practical so that the fibers can be manufactured on a commercially acceptable basis.